1. Field of the Invention
The invention relates to a lifting framework for an industrial truck. The lifting framework has a guide mast and at least one extendible mast. The extendible mast is guided on the guide mast by means of rollers such that it can be moved in the vertical direction between a bottom end position and a top end position.
2. Technical Considerations
Lifting frameworks of the type mentioned above are used in industrial trucks, for example, counterbalance fork trucks or fork-lift reach trucks. A load-bearing means is guided on the lifting framework such that it can be moved in the vertical direction for bearing and raising loads. In most types of industrial trucks, the load-bearing means is located at the front with respect to the main direction of travel. The lateral direction of the lifting framework thus corresponds, by definition, to the lateral direction of the industrial truck. The lifting framework is usually extended telescopically, with at least one extendible mast being guided in a vertically movable manner on a non-raisable vertical mast. The extendible mast is guided on the vertical mast by means of rollers, in each case one pair of coaxial rollers usually being arranged at the top end of the vertical mast and at the bottom end of the extendible mast. The rollers here have a horizontal axis of rotation which is oriented in the lateral direction of the lifting framework and thus of the industrial truck.
The extendible mast is guided laterally on the vertical mast by the lateral surfaces of the above-mentioned rollers. Moments which act on the extendible mast about a longitudinal axis of the industrial truck, and would cause the extendible mast to tilt laterally, are thus supported by the lateral surfaces of the vertically spaced-apart rollers on the mast profiles. It is nevertheless possible, during operation of the industrial truck, for example in the case of asymmetric load action, for the lateral play of the rollers in the mast profiles to give rise to the extendible mast inclining laterally to a slight extent relative to the vertical mast. The greatest amount of inclination on the part of the extendible mast is possible when the extendible mast is located in the region of its top end position, since the vertical spacing between the pair of rollers fastened on the vertical mast and the pair of rollers fastened on the extendible mast is then minimal. The lateral inclination of the extendible mast relative to the vertical mast, this inclination being possible on account of the lateral play of the rollers, is further increased in the case of wide lifting frameworks in which the columns are spaced far apart in the transverse direction of the industrial truck.
An object of the present invention is thus to provide a lifting framework in which the capacity of the extendible mast to incline laterally relative to the vertical mast is at least partially reduced.